The present disclosure relates generally to photodisruption induced by a pulsed laser beam and the location of the photodisruption so as to treat a material, such as a tissue of an eye. Although specific reference is made to cutting tissue for surgery such as eye surgery, embodiments as described herein can be used in many ways with many materials to treat one or more of many materials, such as cutting of optically transparent materials.
Cutting of materials can be done mechanically with chisels, knives, scalpels and other tools such as surgical tools. However, prior methods and apparatus of cutting can be less than desirable and provide less than ideal results in at least some instances. For example, at least some prior methods and apparatus for cutting materials such as tissue may provide a somewhat rougher surface than would be ideal. Pulsed lasers can be used to cut one or more of many materials and have been used for laser surgery to cut tissue.
Examples of surgically tissue cutting include cutting the cornea and crystalline lens of the eye. The lens of the eye can be cut to correct a defect of the lens, for example to remove a cataract, and the tissues of the eye can be cut to access the lens. For example the cornea can be to access the cataractous lens. The cornea can be cut in order to correct a refractive error of the eye, for example with laser assisted in situ keratomileusis (hereinafter “LASIK”).
Many patients may have visual errors associated with the refractive properties of the eye such as nearsightedness, farsightedness and astigmatism. Astigmatism may occur when the corneal curvature is unequal in two or more directions. Nearsightedness can occur when light focuses before the retina, and farsightedness can occur with light refracted to a focus behind the retina. There are numerous prior surgical approaches for reshaping the cornea, including laser assisted in situ keratomileusis (hereinafter “LASIK”), all laser LASIK, femto LASIK, corneaplasty, astigmatic keratotomy, corneal relaxing incision (hereinafter “CRI”), and Limbal Relaxing Incision (hereinafter “LRI”). Astigmatic Keratotomy, Corneal Relaxing Incision (CRI), and Limbal Relaxing Incision (LRI), corneal incisions are made in a well-defined manner and depth to allow the cornea to change shape to become more spherical.
Cataract extraction is a frequently performed surgical procedure. A cataract is formed by opacification of the crystalline lens of the eye. The cataract scatters light passing through the lens and may perceptibly degrade vision. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may increase, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those shorter wavelengths are more strongly absorbed and scattered within the cataractous crystalline lens. Cataract formation may often progresses slowly resulting in progressive vision loss.
A cataract treatment may involve replacing the opaque crystalline lens with an artificial intraocular lens (IOL), and an estimated 15 million cataract surgeries per year are performed worldwide. Cataract surgery can be performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole can be formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (TOL) can be inserted into the remaining lens capsule of the eye.
Prior short pulse laser systems have been used to cut tissue, and have been used to treat many patients. The short pulses have a temporal duration that is short enough to provide optical breakdown with plasma formation to cut tissue. These laser systems rely on very accurate placement of the pulses, and a patient interface may be employed to align the laser with tissue. However, the prior patient interfaces can be somewhat cumbersome for users and may result in increased intraocular pressure in at least some instances, and it would be helpful to provide treatments quickly with less reliance on the patient interface. Variability of the tissue location where optical breakdown occurs may result in tissue cutting that may be somewhat rougher than would be ideal in at least some instances. Work in relation to the present disclosure suggests that prior methods and apparatus used to treat materials such as tissue can use in greater amounts of energy than would be ideal and have less accuracy of the location of optical breakdown than would be ideal. Also, exposure to the treatment beam and ultraviolet light resulting from optical breakdown can be greater than would be ideal in at least some instances. Laser cutting of the cataractous lens can result in the formation of gas bubbles that may interfere with the cutting of subsequent pulses, and treatments with gas formation may result in less complete cutting of the lens tissue than would be ideal.
Some of the prior patient interfaces may provide less than ideal results in at least some instances. Prior patient interfaces that place a flat plate on the eye can alter the shape of the cornea and may result in distortion of the cornea and increases in intraocular pressure. Curved patient interfaces that contact the cornea may result in folds of the cornea that may interfere with cutting of tissue, such as lens tissue in at least some instances. Also, the treatment range over which such prior systems can effectively cut tissue with optical breakdown can be less than ideal in at least some instances.
Some of the prior optical coherence tomography (OCT) systems can provide less than ideal results when combined with a patient interface. For example, work in relation with the present disclosure suggests that at least some of the optical surfaces of the prior patient interfaces can interfere with at least some of the prior OCT measurements of the eye in at least some instances.
Thus, improved methods and systems would be helpful for treating materials with laser beams, such as the surgical cutting of tissue to treat cataracts and refractive errors of the eye.